We all know that when using a tensile testing machine, the tension machine fixture is an indispensable part. Of course, it is a variety of types, fixture according to different test methods, can be roughly divided into: stretching class fixture, compression class fixture, bending class fixture, stripping class fixture, shear class fixture.
The fixture of the tensile testing machine also affects the quality of the tensile testing machine, how to judge the fixture of the tensile testing machine?
Due to the particularity of fixture structure, it is sometimes difficult for us to determine which kind of specimen is more suitable for a fixture, which is usually judged from the following three points:
1. Whether the fixture is convenient and safe to use.
2, whether the clamping is reliable, no slip phenomenon.
3. During the test, the sample has good breakpoint. Data dispersion is small. (That is, sample continuous clamp mouth, inside the clamp mouth, parallel section or outside the standard distance)
6 special situations to watch out for:
1. For materials with large deformation, clamping is difficult due to the large deformation, and the design of the fixture is also a difficult point.
2 for the need to do the test in the high temperature environment, the requirements of the fixture is also very high, both to withstand high temperature, and not deformation, the volume to small, so the general testing machine manufacturers, is also very difficult to do things.
3. The steel wire and steel strand have not been well solved due to the high hardness of the samples, the relatively loose internal structure, the uneven stress in the tensile test process, and the easy wear of the clamps holding the samples. In the past, it was made with aluminum foil. Four pieces of aluminum foil were used in one experiment. Now the tension testing machine jig with spraying emery is adopted, the problem of slipping is solved, but the fracture position is not ideal all the time, 10 samples can only be successful about half.
4. For large batch and high frequency tests, automatic clamping is widely used in foreign countries.
5. For the detection of finished products and semi-finished products, the required fixture is a variety of personalized to meet customer requirements, for all testing machine manufacturers, is a challenge.
6. Commonly used jig names are: universal jig, wire tension jig, rubber tension jig, spring tension jig, sewing thread special jig, terminal special jig and so on.
The fixture material meets the standard：
1. For general metal and nonmetal sample, jig jaw direct contact with the sample, generally choose high quality alloy steel, alloy of high carbon steel or low carbon alloy steel, cold work die steel, and so on, through appropriate heat treatment (quenching tempering, carburizing and quenching, etc.) to increase its strength and abrasion resistance. Sometimes in the jaw with special steel, or in the jaw surface spray corundum, etc.
2. For the fixture of some small test forces, the surface contacting with the sample shall be made of sticky and soft rubber.(for example: the clamping surface of plastic film, fiber, etc.
3. The clip is generally made of high quality medium carbon steel and alloy structural steel, and its mechanical properties are increased by proper heat treatment process.Sometimes in order to reduce the weight of aluminum alloy and other nonferrous metals and special metals.Sometimes cast structures (cast steel, cast aluminum, etc.) are also used.
Based on years of industry service experience, haida international can provide you with opinions or Suggestions on product selection. If you want to get Suggestions on product selection in your industry, or if you encounter problems in test methods and result evaluation, please feel free to contact us.